Part Number:AM3352
Hi,
a customer has in a running project not followed the design deisgn rules for 'RTC timer functionality but not RTC-only mode"
- Connect pin D6 (CAP_VDD_RTC) to +1V1_CORE power rail.
- Connect pin B4 (RTC_KALDO_ENn) to +1V8 instead GND (may use PU resistor or direct connection).
- Connect pin C5 (EXT_WAKEUP) to GND (using this signal on the connector XM2 make sense only for “RTCmode”,
but obviously your schematic don’t support this mode (because you don’t have “Always-On” 1.8V power
rail to supply VDDS_RTC power domain).
- The RC circuit R57/C50 connected on pin B5 (RTC_PWRONRSTn) maybe matched the minimal requirements
for the RTC reset, but by my opinion the better solution is using the same reset as PORz but with 1.8V level.
For this purpose you can use resistive divider from eSOM_PowerEnable net to RTC_PWRONRSTn input.
Other option (better by my) is if change eSOM_PowerEnable logic level to 1.8V instead 3.3V (supply the PU
R38 on page 4 from +1V8 instead +3V3) and directly connect it to both resets together (PWRONRSTn works
correctly with 1.8V or 3.3V level independently of VDDSHV6 power supply)
What is the risk, if they stay with the layout?
Best regards